We aim to assess the relative efficacy of coronary bypass graft (CABG) surgery and percutaneous transluminal coronary angioplasty (PTCA) for treatment of severe symptomatic coronary artery disease. We propose to compare the two treatments by assessing the three primary endpoints of (1) relief of symptoms; (2) patency of the treated vessel; and (3) cardiac events, including acute infarction, congestive heart failure and death, at one year and at four to six years after treatment. A single clinical trial of 1800 patients, with 900 in the CABG and PTCA arm respectively, is suggested, with a randomization scheme in which severe stable angina, unstable angina and postinfarction angina are stratified prior to randomization. Included in the trial will be patients with severe angina and multivessel disease; up to 65 years of age, with EF greater than or equal to 35%; without prior PTCA or CABG; and without 100% major vessel occlusions distributing to viable myocardium. Evaluation will include clinical outcome assessments, exercise stress testing and cardiac catheterizations at one year and at final follow-up. Secondary endpoints are left ventricular function, the functional status of the patient, progress of disease in the native coronary arteries and the need for revascularization procedures. It is expected that patients will require repeat procedures, and a high crossover rate may occur. Hence, the final assessment of efficacy relative to the endpoints of the study will be based upon the several years strategy of care initiated by either PTCA or CABG surgery. The protocol also assesses cumulative dollar cost of each treatment arm as defined by the initial therapy performed, including the cost of all cardiac procedures and hospitalization over the full follow-up period. This economic analysis is viewed as an important secondary endpoint of the study. A registry of all potentially randomized patients from the clinical sites is also proposed, and will serve to provide clinical outcome data on a larger number of patients with CAD, and to compare the randomized patients to the potentially randomizable. In final analysis, the BARI trial should provide an answer to the important question of relative efficacy of the two treatment strategies, CABG surgery and PTCA, for severe symptomatic coronary disease.